Disc drives of the type known as "Winchester" disc drives or hard disc drives are well known in the industry. Such disc drives record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator housing opposite to the coil, the actuator housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the heads are moved radially across the data tracks along an arcuate path.
The head suspensions mentioned above are typically formed from thin stainless steel foil. In order to provide a robust connection between the head suspension and the actuator head mounting arms, the attachment end of the head suspension is typically welded to a relatively thick mounting plate which includes features intended to cooperate with mating features on the actuator head mounting arms to attach the head suspensions to the actuator.
By far the most common head suspension mounting method in current use is swage mounting. Swage mounted head suspensions include mounting plates that are formed with a cylindrical swage boss. Typically, the entire array of head/suspension assemblies is placed in cooperative arrangement with the actuator head mounting arms, with the swage bosses of the head suspension mounting plates inserted into openings in the actuator head mounting arms. A swaging tool, consisting of a ball feature having a diameter slightly larger than the inner diameter of the swage bosses, is then passed through the entire vertically aligned stack of swage bosses, expanding the swage bosses into firm contact with the inner diameters of the openings in the actuator head mounting arms. Thus, swage mounting of the head/suspension assemblies is simple and economical for use in high volume manufacturing environments.
Swage mounting of head suspensions does, however, produce potential problems. Firstly, the plastic deformation of the swage bosses during the swaging process induces large mechanical stresses in the material of the mounting plates, and these mechanical stresses can lead to deformation of the planar portion of the mounting plates to which the thin head suspensions are welded. Such deformation can lead to uncontrolled variation in the pitch and roll static attitudes of the entire head suspension/head assembly, adversely affecting the data recording/recovery performance of the entire disc drive.
Secondly, since the swage mounting plates must be located on the upper and lower surfaces of the actuator head mounting arms, and since certain minimal vertical dimensions of the various components must be maintained to provide the necessary mounting strength, swage mounting dictates that the vertical spacing between the elements of the head/disc stack has a finite minimum. In order to provide the maximum amount of storage capacity in a disc drive, designers seek to incorporate the greatest number of heads and discs possible within industry-defined physical form factors, or, alternatively, to develop ever smaller form factors. Thus, swage mounting imposes limits on the number of heads and disc that can be fitted into a defined physical package, and may impose limits on the total storage capacity of the disc drive.
Finally, swage mounting, by definition mechanically deforms the associated components when it is performed. If, after assembly, a faulty component is discovered, it is first difficult to disassemble a swage mounted head suspension assembly without damaging other "good" components. Additionally, reinsertion of a replacement swage mounted head suspension into a head mounting arm that has already been stressed by a previous swaging operation may result in less than optimal mounting force, leading to undesirable variation in the finished product.
For these and other reasons to be noted below, a need clearly exists for an alternative to swage mounting of the head suspension assemblies in a disc drive.